1. Field of the Invention
The present invention relates to an apparatus and a method for controlling an engine clutch of a hybrid electric vehicle. More particularly, the present invention relates to an apparatus and a method for controlling an engine clutch of a hybrid electric vehicle that controls a standby hydraulic pressure of an engine clutch differently according to a mode changing condition when the driving mode of the hybrid electric vehicle is changed from an electric vehicle (EV) mode to a hybrid electric vehicle (HEV) mode.
2. Description of Related Art
As is well known, according to demands for improving fuel efficiency for a vehicle and stronger on board diagnosis regulations for exhaust gas, an environmentally-friendly vehicle has been provided.
The environmentally-friendly vehicle generally includes a fuel cell vehicle, an electric vehicle, a plug-in electric vehicle, and a hybrid electric vehicle, and includes one or more motors and engines.
The hybrid electric vehicle can be classified as two types depending on the power source of the engine and the motor. A parallel type of hybrid electric vehicle is driven by mechanical power of the engine directly and uses electric power of the motor in case of need. On the other hand, a straight type of hybrid electric vehicle is driven by electric power of the motor which is converted from mechanical power of the engine by a generator.
The hybrid electric vehicle may be driven in a driving mode such as an electric vehicle (EV) mode which is a true electric vehicle mode using only power of the motor, a hybrid vehicle (HEV) mode which uses rotational force of the engine as main power and uses rotational force of the motor as auxiliary power, and a regenerative braking (RB) mode for collecting braking and inertial energy during driving by braking or inertia of the vehicle through electric generation of the motor to charge the battery.
Herein, the hybrid electric vehicle changes the driving mode from the EV mode to the HEV mode by coupling an engine clutch after the engine starts according to a demand torque of a driver, a battery state of charge, and so on.
The engine clutch transmits power between the engine and the motor, and is coupled by increasing a standby hydraulic pressure to a lockup hydraulic pressure after the engine starts and an engine speed and a motor speed are synchronized.
However, the standby hydraulic pressure generated at the engine clutch is different due to hardware deviations of the engine clutch and a solenoid valve. Thus, when the standby hydraulic pressure is not controlled equally, drivability of the hybrid electric vehicle may be deteriorated according to a lack of starting power when the driving mode changes from the EV mode to the HEV mode.
The conventional art controls the standby hydraulic pressure to about 0.2 bars lower than a practical hydraulic pressure for solving hardware deviations of the engine clutch and the solenoid valve.
However, the practical hydraulic pressure cannot be estimated because of hydraulic pressure reactivity while an engine clutch is being coupled.
Therefore, responsiveness for a kick-down request cannot be secured because of hydraulic pressure reactivity when the engine clutch is coupled according to a kick-down request during the EV mode.
Moreover, the engine clutch is coupled after synchronizing the engine speed and the motor speed, so the responsiveness is delayed according to a delay of hydraulic pressure reactivity when a demand torque of the driver is high.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.